Pluto is still a planet. This comforts me, for some reason. The real story here, though, is the difficulty, or maybe impossibility, of coming up with a definition of what is and is not a planet that will satisfy everyone. The decision for now is to say that a planet is any object that orbits a star instead of another planet and exerts enough gravitational force to form itself into a sphere. This avoids the counterintuitive effect of demoting Pluto, but it also means that Ceres, a large round asteroid, is now a planet, as is Charon, Pluto’s biggest moon, because strictly speaking Pluto and Charon both orbit the sun while sharing a gravitational axis — sort of like two guys in a bar fight with their hands around each other’s necks, spinning around each other and knocking over the tables.

Nietzsche says it best: only that which has no history can be defined. Which I’ve always taken to mean, all complex classes of things come to share a lingustic/conceptual identity only by virtue of a shared history — historical relationships between the things themselves, and historical relationships between the people talking about them.

Take jazz. In terms of musical style, there is almost nothing in common between Cecil Taylor and Louis Armstrong except improvisation, and even there, their respective ideas of improvisation are so different they might as well belong to two entirely different cultures. But if you asked any jazz fan — or any competent record-store clerk — what part of the store to stock “Unit Structures” and a Hot Fives record in, they’ll say “jazz.” Cecil Taylor is following a certain train of thought put in motion by Louis Armstrong (among others), but, as in a game of “telephone,” that thought comes to us having followed a complicated series of transactions and in the process has changed out of recognition. Wittgenstein uses the metaphor of the rope to think about the paradoxical way things can share a categorical identity while having nothing in common with one another. A rope is made up of thousands of strands that are twisted together to make the rope. The rope runs without break from point A to point Z, but there is no one strand within the rope that runs from A to Z. The rope, in the case of jazz, is history or tradition; the strands are the individual practices of artists like Taylor or Armstrong and the arguments of fans and critics. Some of those critics, like Stanley Crouch, simply do not accept this kind of definition-by-contingency. Over the years Crouch has argued that there is or should be a list of stylistic qualities without which music cannot be considered jazz: swing, improvisation, the “Latin tinge,” and I forget the others.

In this sense Crouch comes at the problem of definition in much the same way as many of the scientists quoted in the above article. Scientists need to construct categories that are valid as analytical tools for every potential instance of a class of things, including those we haven’t encountered yet. (And as time goes on, chances are we’ll find more and more planets outside the solar system.)

From this point of view, the historical rule-of-thumb categorization of planets we’ve collectively evolved to think about our own cosmic neighborhood is unscientific. From point of view accepts the groupings generated from within history, the scientific style of classification seems arbitrary. I guess the point is to think about which style of classification works best for which kind of knowledge, and we could have an argument about that, but for now what’s interesting to me is how the planet controversy marks a point where two fundamental ways of classifying the world collide.